The National Electronics Manufacturing Initiative (NEMI) has endorsed Sn—Ag—Cu as the lead-free solder standard for the electronics industry. New solder materials have been reported by microalloying of grain refining elements into Sn—Ag and Sn—Cu—Ag systems to achieve better mechanical properties. [1-3]. These materials are generally made by co-milling of different powders. Milling of materials such as Sn—Ag and Sn—Ag—Cu does not control particle size, impurities, composition, and homogenity.
Another method used to deposit lead-free solder films is electroplating. Unfortunately, electroplating does not control the composition accurately, and is not widely demonstrated to achieve ternary compositions.
Therefore, it can be seen that a need exists for a solder deposition process that can control the composition accurately, as well as be free from any impurities which is inherent in processes such as milling. The invention described herein can serve as an excellent bonding technology for bonding chip to package interconnects.
These interconnects can provide improved electrical performance while lowering the stresses at the interfaces by orders of magnitude. It is to such a structure, being a high-aspect-ratio metal-coated polymer structure, that the present invention is primarily directed. This technology when used in conjunction with polymer-based structures can also simplify the processing steps and result in tremendous cost reductions.